Stents are expandable devices inserted into arteries via angioplasty techniques that keep a blood vessel open. They are typically open tubular structures having, for example, struts and ribs that allow expansion when an interiorly placed balloon is inflated. The stents are typically made of metal although other materials are possible, and are designed to be inflated with sufficient pressure to make close contact with the wall of the lumen in the artery being treated. Manufacturer recommended pressures for expansion of standard stents are typically in the range of from 4 to 16 atmospheres.
Current clinical practice is to position a balloon and stent in the required location by observation, for example, using angiographic x-ray techniques. The balloon is typically filled with a solution of saline and x-ray contrast agent. The angiogram presents a one-dimensional cross-sectional view of the artery with relatively poor spatial resolution, which is commonly the case, as the lumen of an artery does not necessarily have a circular cross-section, especially in atherosclerotic sections where it is likely to be an irregular shape. Although the physician may view the artery from more than one angle, the information provided by angiography is limited and insufficient to provide an accurate assessment of the size to which the stent should be inflated.
Angiography is also used in current clinical practice to determine the degree to which an artery is narrowed. Narrowing of the artery is called stenosis and is illustrated in FIG. 1A. Stenosis is caused by the buildup of plaque 14 commonly referred to as lesions on an interior area of an artery wall 10. This in turn decreases a cross-section of the lumen 16 through which blood flows 12. In FIG. 1A, the narrowing caused by an atherosclerotic plaque 14 is of the order of 70% in the longitudinal view and, as such, would likely be treated with balloon angioplasty and stent placement. The cross-sectional view of FIG. 1A, shown at lower inset, illustrates the irregularly shaped lumen 16. As illustrated, plaques 14 commonly form with increased frequency at or very near to bifurcations of the artery 18.
In current, practice, the cardiologist estimates the degree of narrowing as compared to the expected dimension of an open lumen. Based on this estimation, the cardiologist then determines whether an angioplasty or coronary artery bypass graft (CABG—bypass surgery) is required to improve blood flow. Such stenotic lesions as plaques 14 are commonly treated using balloon angioplasty, as illustrated in FIG. 1B. A balloon catheter 22 includes a dilation balloon 20 attached to a guidewire 24 to navigate through the artery. The dilation balloon 20 is inserted at the area of the lesion 14 and inflated to increase the luminal size 16. Following dilation, stents which may be deployed by the use of the balloon catheter 22 are commonly placed at the site of the lesion to prevent stenosis at a later time (restenosis).
As known in the field, accurate stent expansion is critical to the success of an angiography procedure. For example, the over-expansion of a stent can cause rupture of the blood vessel. Conversely, under-expansion of a stent leaves areas or gaps between a stent structure and lumen wall which can lead to thrombosis.
Accordingly, there is a need for a device, system, and method which provide for accurate measurement of the dimensions of a luminal space of an artery thereby allowing for the determination of the size to which a stent should be expanded. There is also a need for combining a device for determining the location of a lesion with a means for deploying a sent. Such a combined device requires connectors which allow the locating device to identify a lesion, disconnect from an instrument box allowing a secondary device to be slid over the locating device so that the secondary device may act on the lesion, for example, deploy a stent, and reconnect to the instrument box to allow observation of the deployed stent.